This invention relates to a liquid level sensing device or "sender" or transmitter such as for indicating the amount or level of petrol or other liquid e.g. in a motor car fuel tank.
For this purpose it is known to use differential transformers and similar devices wherein a float moves an armature in a solenoid wired in circuit with a gauge responsive to changes of inductance in the solenoid. These so-called "magnetic" devices, although generally linear in nature, are quick to respond, which may often be a disadvantage when the level is subject to rapid temporary fluctuations due to bumping, rapid starts and stops, and other transitory irregularities in the motion of a vehicle in which it is incorporated.
Another known contrivance used a float cooperable with a rheostat to provide a variable current through a gauge, which may be of the so-called "thermal" type wherein the current heats a bi-metallic strip to which the gauge pointer is mechanically related in some suitable way. This has the advantage of a slow response and so tends to indicate an average level over an interval longer than a normal "sloshing" period, but it is generally non-linear in operation.